A xenocryst is a crystal that is not formed from the magma in which it is found but has been incorporated into the magma from surrounding rocks. Xenocrysts are significant in petrology for understanding magma contamination, the processes of magma assimilation, and the interactions between different rock types during magmatic activity.
Reference: Smith, D. (1992). “Xenocrysts in Kimberlites and Other Volcanic Rocks.” Journal of Volcanology and Geothermal Research, 50(1-2), 83-98.